This invention relates to a circuit for maintaining compatibility between different image signal recording/reproducing systems during reproduction. This invention relates more particularly to an improvement on the invention titled "Improved image signal recording system" of U.S. patent application Ser. No. 07/659,029, filed Aug. 17, 1990 by this applicant.
At present, the image signal recording/reproducing system used in the home, records image signals on video cassette tapes according to one of several methods. Conventional VHS systems (referred to as standard VHS system) have insufficient horizontal resolution, and the image quality is degraded. Generally, the improved VHS system, called super VHS (S-VHS), provides an improved image quality by recording the image signal of full bandwidths on the video cassette tape.
Such systems require superior quality of tapes and recording/reproducing systems. However, the above S-VHS system is incompatible with a VCR of the standard VHS system. A VCR according to the S-VHS system is able to reproduce images recorded by the VCR's of both the S-VHS and the standard VHS systems, but a VCR according to the standard VHS system is unable to reproduce images recorded by the S-VHS system.
Therefore, the above U.S. patent application Ser. No. 07/569,029 removes the conventional drawbacks stated above, and provides an improved image signal recording system designed to have reverse compatibility with the standard VHS method.
However, the image signal recording system described in the above U.S. patent application Ser. No. 07/569,029 is unable to obtain the desired specific characteristics by analog processing of the signal in the de-emphasis unit during reproduction.
Of particular note, in the above system, when the adaptively folded signal passes through the de-emphasis unit connected to the input f the decoder, accurate reproduction of the recorded signal is difficult, and if the characteristic of the de-emphasis unit is not good, high-frequency components of the adaptively folded signal are degraded. Moreover, when the above adaptively folded signal is unfolded in the unfolding unit, the high frequency components in the signal bandwidths unfolded in double are attenuated, reducing resolution during reproduction.